Theorem impor

Description: An equivalent formula for implying a disjunction. (Contributed by Giovanni Mascellani, 15-Sep-2017)

	Ref	Expression
Assertion	impor	|- ( ( ph -> ( ps \/ ch ) ) <-> ( ( -. ph \/ ps ) \/ ch ) )

Proof

Step	Hyp	Ref	Expression
1		imor	|- ( ( ph -> ( ps \/ ch ) ) <-> ( -. ph \/ ( ps \/ ch ) ) )
2		orass	|- ( ( ( -. ph \/ ps ) \/ ch ) <-> ( -. ph \/ ( ps \/ ch ) ) )
3	1 2	bitr4i	|- ( ( ph -> ( ps \/ ch ) ) <-> ( ( -. ph \/ ps ) \/ ch ) )